Treason

Part of speech: noun (n.)

1. The offense of attempting to overthrow the government of the state to which the offender owes allegiance, or of betraying the state into the hands of a foreign power; disloyalty; treachery. The treason of the murthering in the bed. Chaucer.

2. Loosely, the betrayal of any trust or confidence; treachery; perfidy. If he be false, she shall his treason see. Chaucer. Petit treason. See under Petit.